The present invention relates to an actuator controller for electromagnetic valves, and more specifically concerns a controller for an actuator which drives a valve of an engine which is used, for example, in an automobile and a boat or the like.
Among valve operating systems which are driven by an electromagnetic actuator and called electromagnetic valve, the mechanism that drives a valve connected to an armature has used the following method for driving electromagnets (hereinafter, referred to as a xe2x80x9csolenoid actuatorxe2x80x9d or simply xe2x80x9cactuatorxe2x80x9d) . Here, electric power is alternately supplied to a pair of opposing electromagnets to drive a movable iron piece, that is, an armature interposed between a pair of springs, to which an offset load has been applied.
1) A magnetic attractive force applied by one of the actuators to the armature overcomes a repulsion force of a pair of springs, thereby attracting the armature to a seating position. This armature (valve) is released from the seated state with stoppage of the power supply to the actuator as a turning point, and starts displacement in a cosine manner by the function of a pair of springs.
2) A catch current supplied to the other of the actuators at a timing corresponding to the displacement of the armature produces magnetic flux generating an attractive force.
3) As the armature approaches the other of the actuators that is generating the magnetic flux, the magnetic flux abruptly grows so that work by the attractive force of the other of the actuators overcomes the sum of a small work drawing the armature back by residual magnetic flux of the one of the actuators and a mechanical loss, which is a greater part of the work. Thus, the armature is attracted to seat on the other of the actuators.
4) As seating of the armature takes place, a holding current for holding the armature is supplied to the other of the actuators at an appropriate timing to maintain the armature in the seated position.
During a period of time for holding the armature, the holding current is normally supplied with a PWM (Pulse Width Modulation) scheme. Its specific method is described in U.S. patent application Ser. No. 09/534,054 filed on Mar. 24, 2000, which is incorporated herein by reference.
In the valve operating system of an ordinary automotive engine, the amplitude of the displacement of an armature interposed between a pair of opposing electromagnets can reach 6 to 8 mm. Actual valves experience secular changes in an electric, magnetic and/or mechanical systems, and also experiences unevenness in the operation. The following three points are the main causes.
1) The mechanical loss of the valve varies as the engine load fluctuates so that the magnitude of the mechanical work required for seating the armature varies, thus affecting the operation of the armature.
2) Since it is difficult to control a magnetic attracting force for holding the armature in the seated position, there is variation in the residual magnetic flux when the armature is released. As a result, the dead time from the time when the power supply to the actuator is stopped to the time when the armature actually departs from the actuator varies, affecting the subsequent control of the valve timing.
3) Change of the magnetic characteristic of magnetic material causes greater or smaller attractive force even at the same driving current, thereby making the armature holding operation unstable.
As a specific example, behavior of an electromagnetic actuator working at a high speed as used in the valve driving system of an engine will be described with reference to FIG. 3. The left vertical axis indicates the amount of lift (mm) of the armature as well as current (in ampere) to be supplied to the actuator, the right vertical axis indicating attractive force (N) and voltage (V) to be applied to the actuator. The arrows in the drawings indicate which scale is to be referred to, the right vertical axis or the left vertical axis.
At time 0, the armature is released from one of the actuators and starts displacement toward the other of the actuators by the work of a pair of springs. At time 3 ms, constant voltage (60V) starts to be applied to the other of the actuators causing magnetic flux to grow. During a period of 2.2 ms from the time 3ms to 5.2 ms, a constant voltage xe2x80x9ccxe2x80x9d is applied, and thereafter, a switching voltage waveform is applied by the PWM (Pulse Width Modulation) controller such that the current value becomes constant (0.45 A) as seen in curve xe2x80x9cbxe2x80x9d. In FIG. 3, the voltage is indicated by a moving average value of switching voltage waveform.
In this example, the armature seats on the yoke surface 200 xcexcs before the application of constant voltage is terminated. When the gap between the armature and the seating surface becomes small, magnetic flux which crosses the armature abruptly increases thereby generating a very large attractive force. In FIG. 3, a bold straight line xe2x80x9cfxe2x80x9d of the level of 300(N) indicates the minimum attractive force (necessary holding force) needed for holding the armature in the seated position, which depends on the hardness of a pair of springs holding the armature.
As is apparent from FIG. 3, an abrupt increase in the attractive force xe2x80x9chxe2x80x9d before and after seating generates an overshoot over the necessary holding force. After the seating, the electric power supplied to the actuator is switched to provide a constant-current, and control is performed so as to generate slightly larger attractive force than the necessary holding force. But this control has the following problems.
In case of an automotive engine, the number of revolutions ranges from 600 to 7,000 rpm, and the armature holding time also greatly changes in proportion thereto. On a high-revolution side, the armature must be released quickly, thus making it impossible to secure the time required to generate slightly larger attractive force than the necessary holding force. As a result, the amount of overshoot varies due to an abrupt change in the attractive force before and after seating, correspondingly generating variations in the magnitude of the attractive force when the armature is released.
When the amount of overshoot is large and the attractive force at a point in time when the armature should be released is larger than the necessary holding force, the magnetic energy that the actuator has at this point in time is maintained in the form of eddy current, which is not released instantaneously. Therefore, between the time when release control of the armature starts and the time when the armature is actually released from the yoke is a time lag, that is, dead time of the armature release. In the example of the drawing, the dead time is 0.45 ms, but this time varies depending upon the amount of overshoot. These variations in the dead time cause differences in the valve timing, greatly affecting the output performance of the engine.
Therefore, it is an object of the present invention to provide control technique for quickly correcting overshooting of attractive force generated when the armature is seating, so as to provide an appropriate attractive force. It is also an object of the present invention to provide a control technique for providing an appropriate attractive force to the armature by compensating for variations in the lift timing of the armature.
An actuator according to a first aspect of the invention comprises: a pair of springs which act in opposite directions; an armature which is connected to the springs and is supported in a neutral position provided by the pair of springs in an inactivated state, the armature being coupled to a mechanical element; a pair of electromagnets which drive the armature between a first terminal position and a second terminal position; estimating means for estimating magnetic flux to be generated by the electromagnet attracting the armature when the armature is driven from one of the terminal positions to the other of the terminal positions; and means for switching the electromagnet from the attractive operation to the holding operation in response to the magnetic flux reaching the target overshoot value.
The electromagnet is switched to the holding operation when the gross magnetic flux of the electromagnet attracting the armature reaches the target overshoot value, and therefore, the phenomenon in which the electromagnet maintains residual magnetic energy greater than necessary lessens. This leads to reduction in the variations in dead time in releasing the armature.
According to another aspect of the invention, there is provided an actuator, further comprising means for applying reverse voltage to the electromagnet generating an attractive force, thereby decreasing the magnetic flux from the maximum value to a value required for holding the armature, the reverse voltage being determined based on the maximum value of the magnetic flux estimated by the estimating means.
In order to decrease the magnetic flux of the electromagnet generating an attractive force from the maximum value to a value required for holding the armature, a reverse voltage is applied to the electromagnet. The attractive force of the electromagnet is speedily lowered to the holding force. Therefore, the armature can be released from the electromagnet at a fast timing enabling the actuator to be actuated at high speed.
An actuator controller according to further another aspect of the invention comprises: a pair of springs which act in opposite directions; an armature which is connected to the springs and is supported in a neutral position provided by the springs in an inactivated state, the armature being coupled to a mechanical element; a pair of electromagnets which drive the armature between a first terminal position and a second terminal position; magnetic flux estimating means for estimating magnetic flux generated by the electromagnet attracting the armature when the armature is driven from one of the terminal positions to the other of the terminal positions; timing estimating means for estimating timing of the armature lift when the armature is driven from one of the terminal positions to the other of the terminal positions; and control means for controlling period of applying voltage to the electromagnet for attracting the armature in accordance with the magnetic flux estimated and the timing estimated.
Since the time for applying voltage to the electromagnet is controlled by estimating the magnetic flux to be generated by the electromagnet and the timing of the armature lift, the magnetic flux required for attracting the armature can be generated even if the lift timing of the armature is delayed.
According to another aspect of the invention, there is provided an actuator controller further includes means for detecting the maximum current value which flows through the electromagnet.
It is possible to estimate the lift timing for the armature by a simple method of detecting the maximum current value which flows through the electromagnet.